Insights on the activity-selectivity trade-off in iron-containing nitrogen-doped carbon catalyst via cobalt addition for oxygen reduction reaction in alkaline medium

Abstract

Iron-based noble-metal-free electrocatalysts exhibit impressive performance and stability for the Oxygen reduction reaction (ORR) in alkaline media, but face challenges. This study investigates the impact of Co addition to Fe in nitrogen(N)-doped carbon (Fe/NC) catalysts prepared via one-pot synthesis involving direct pyrolysis of the metal (M) and 2,4,6-tris(2-pyridyl)-s-triazine complexes (M-TPTZ) on carbon. Comprehensive characterization reveals N-doped carbon structures with single-atom sites and metal oxides, with M-Nx centers mainly in carbon pores and metal oxides on the carbon surface. N2 adsorption/desorption experiments and electrochemical surface area (ECSA) reveals that Co introduction enhances the catalyst surface area. Moreover, Co addition alters nitrogenated species distribution, affecting catalytic activity. Electrochemical studies rank catalytic activity as Fe/NC < Co/NC < CoFe/NC, while rotating ring-disk electrode (RRDE) investigations show mixed 2 and 4 electrons pathways. Fe/NC follows a 4e- pathway with minimal HO2− production, while Co-containing catalysts suggest a mixed (2e- + 2e-) pathway with an average of 3.75 electrons involved. This divergence highlights nuanced electrochemical characteristics of Fe- and Co-based materials, emphasizing the need for in-depth characterization.